Field of the Invention
This invention relates to electric motors and particularly to stepping motors.
Generally, a stepping motor includes a rotor with outwardly-projecting peripherally-spaced longitudinally-extending rotor teeth which interact with inwardly-projecting peripherally-spaced longitudinally-extending stator teeth. The latter are mounted in sets on peripherally-spaced inwardly-projecting longitudinally-extending stator poles such that the stator teeth on one pole may align with the opposing rotor teeth while teeth on another pole are partially misaligned with the rotor teeth and stator teeth on the next peripherally spaced pole align with the valleys between opposing rotor teeth. In so-called "hybrid" motors, rotors contain two axially aligned sections with the teeth of one section aligned with the valleys of the other section. A permanent magnet between the two rotor sections magnetizes the sections in opposite polarities. Appropriately energizing coils on the stator poles causes an interaction between the stator and the teeth that turns the rotor. In so-called variable reluctance stepping motors, the rotor with its rotor teeth is composed of soft magnetic material. The stator coils form a rotating field that moves the rotor incrementally. Such motors have limited efficiencies and other disadvantages.
Attempts have been made to increase the efficiencies of such motors, and to reduce such disadvantages as noise generated by them, by making the pitches on the stator teeth different from those on the rotor teeth. Attempts have also been made to increase torque by intensifying magnetic fields with stronger permanent magnets. Further efforts have been directed toward various techniques of energizing stator windings. However, the basic power and efficiency available from such motors has been limited.
An object of this invention is to overcome the defficiencies of existing motors.
Another object of the invention is to provide an improved motor having higher torque for a given coil current.